Conductive lithographic polymer and method of making devices using same

ABSTRACT

A conductive photolithographic film and method of forming a device using the conductive photolithographic film. The method includes depositing a conductive photolithographic film on a top surface of a substrate; and patterning the conductive photolithographic film to create a desired circuit pattern using a lithographic process. The conductive photolithographic film comprising about 50% to about 60% of a mixture of epoxy acrylate, a thermal curing agent, and a conductive polymer; about 20% to about 30% of a lithographic reactive component; about 10% to about 15% of a photo-active material; and about 3% to about 5% of additives that enhance conductivity of the conductive photolithographic polymer.

The present application is a divisional of U.S. patent application Ser.No. 10/938,161, filed Sep. 9, 2004, now U.S. Pat. No. 7,279,268 entitled“A Conductive Lithographic Polymer and Method of Making Devices UsingSame”, currently allowed. The U.S. patent application Ser. No.10/938,161 is hereby incorporated herein by reference.

BACKGROUND

Embodiments of the present invention relate to a conductive lithographicpolymer and method of making interconnection and conductive features fordevices incorporating the conductive lithographic polymer.

An integrated circuit is an interconnected ensemble of devices formedwithin a semiconductor material and within a dielectric material thatoverlies a surface of the semiconductor. Devices which may be formedwithin the semiconductor include transistors, bipolar transistors,diodes and diffused resistors, to name a few. Devices which may beformed within the dielectric include thin-film resistors and capacitors.Silicon or silicon comprising material is typically used as thesubstrate for these devices.

Typically, more than 100 integrated circuit die (IC chips) areconstructed on a single 8-inch diameter silicon wafer. The devices areinterconnected by conductor paths (also referred to as metalizationlayer) formed within the dielectric. Typically, two or more levels ofconductor paths, with successive levels separated by a dielectric layer,are employed as interconnections. In current practice, metalizationlayers, typically made of copper, are formed on dielectric layers toestablish the conductor paths. Examples of processing methods to formthe metalization layers include chemical vapor deposition (CVD),physical vapor deposition (PVD), and electrochemical deposition.Electrochemical deposition of copper has been found to provide the mostcost-effective manner in which to deposit a copper metalization layer.In addition to being economically viable, such deposition techniquesprovide substantially conformal copper films that are mechanically andelectrically suitable for interconnect structures.

An example of an electrochemical deposition is described (FIGS. 1A-1E).First, an electroless copper plated layer 102 is formed on an insulatinglayer 104 of a substrate 106, which may include thereon conductivefeatures or devices 108 (FIG. 1A). The insulating layer 104 includesthrough holes or vias 110 to enable connection to the conductivefeatures 108. The insulating layer 104 is typically an insulating layerwhich is interposed between conductor patterns formed on multiple layersfor the purpose of ensuring the electrical insulation between theconductor patterns.

Next, a layer of photoresist layer 112 is patterned on the electrolesscopper plated layer 102 as shown in FIG. 1B. Next, an electrolyticcopper plated layer 114 is formed on the exposed electroless copperplated layer 102 as shown in FIG. 1C. The electroless copper platedlayer 102 is used as an electrical feed or seed layer for theelectrolytic plating layer 114.

Next, the photoresist layer 112 is removed as shown in FIG. 1D. Next,the exposed electroless copper plated layer 102 is removed as shown inFIG. 1E by using a copper etching solution. Typically, an alkali etchingsolution is used as the etching solution. Due to the foregoing, aconductor pattern 116, in which the electrolytic copper plated layer 114is laminated on the electroless copper plated layer 102, can be formedon the insulating layer 104. This process is typically repeated over andover for a formation of a multilayered device.

The current practice causes devices (e.g., printed circuit boards) to befabricated with a long process throughput time because of the timeconsuming for film lamination to complete the patterning of theconductive layers. Layers of photoresist need to be used, layers ofelectroless plating and electrolytic plating have to be used, andremoved at each step. In addition, various control systems are neededfor chemical solutions to maintain line stability, for instance, inelectroless plating process there is a need to control accurately andcarefully the amount to be deposited and as well as controlling thethickness of the electroless plating. The fabrication process fordevices thus becomes time consuming and costly.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention are illustrated by way ofexample and not by way of limitation in the figures of the accompanyingdrawings in which like references indicate similar elements. Theinvention may best be understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention. It should be noted that references to “an”or “one” embodiment of the invention in this disclosure are notnecessarily to the same embodiment, and they mean at least one. In thedrawings:

FIGS. 1A-1E illustrate an example of a current practice of forming aconductor path for a device using electrochemical process;

FIGS. 2A-2E illustrate an exemplary method of forming a conductor pathin accordance to the embodiments of the present invention; and

FIGS. 3A-3D illustrate another exemplary method of forming a conductorpath in accordance to the embodiments of the present invention;

DETAILED DESCRIPTION

Exemplary embodiments are described with reference to specificconfigurations and techniques. Those of ordinary skill in the art willappreciate the various changes and modifications to be made whileremaining within the scope of the appended claims. Additionally, wellknown elements, devices, components, circuits, process steps and thelike are not set forth in detail.

Exemplary embodiments of the present invention pertain to a conductivelithographic polymer and method of fabricating devices (e.g., a printedcircuit board) with interconnection and conductive featuresincorporating the conductive lithographic polymer. Conductive traces andconductive paths are used throughout fabrication processes of devices.For examples, devices are formed on substrates and are interconnected toone another through insulation layers and conductive paths ormetalization layers. As previously discussed, electrochemical is one ofthe well-known methods that are widely practiced for making suchconductive paths. The conventional methods commonly require multipleetching and lithographic steps in fabricating the conductive paths forthe semiconductor devices. The currently practice requires longthroughput time and incurs extensive cost for making the devices.

Exemplary embodiments of the present invention disclose a conductivelithographic polymer that can be used to fabricate conductive paths,metalization layers or other conductive features for the semiconductordevices. As used herein, a conductive lithographic polymer can be asynthetic material that includes an intrinsically conductive polymer anda polymer having optical properties. A conductive lithographic polymercan also be a material that includes a lithographic polymer and aconducting polymer that includes a physical mixture of a nonconductivepolymer with a conducting material such as a metal or carbon power. Aconductive lithographic polymer can also be a material that includes alithographic polymer and a conducting polymer that includes a physicalmixture of a conductive polymer with additional conducting material suchas a metal or carbon power added to the mixture to enhance theconductivity of the conductive polymer. The conductive lithographicpolymer can be used as a photoresist material due to its opticalproperties. Normal lithographic methods can be used to pattern theconductive lithographic polymer. The lines, traces, or paths formedusing the conductive lithographic polymer can then be used as conductivetraces or paths, or metalization layers due to its conductiveproperties. The conductive lithographic polymer thus may replace theordinary photoresist layer plus the electroless plating layer previouslymentioned or may replace the ordinary photoresist layer, the electrolessplating layer, and the electrolytic plating layer previously mentioned.The conductive lithographic polymer may also be used to form otherconductive traces and/or metalization layers currently being formedusing metals such as copper.

In one embodiment, the conductive lithographic polymer is a mixture thatcomprises of (1) about 50% to about 60% (weight percentage) of a mixtureof epoxy acrylate, a thermal curing agent, and a conductive polymer; (2)about 20% to about 30% (weight percentage) of a lithographic reactivecomponent; (3) about 10% to about 15% (weight percentage) of aphoto-active material; and (4) about 3% to about 5% (weight percentage)of additives that enhance or serve other function conductivity of theconductive photolithographic polymer.

The ratio of epoxy acrylate, a thermal curing agent, and a conductivepolymer may be varied depending on the desired level of conductivity ofthe conductive lithographic polymer and the conductivity of theconductive polymer used for the mixture.

In one embodiment, the thermal curing agent is selected from a groupconsisting of imidazole, imidazole derivative, 2-methylimidazole,2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole,4-phenylimidazole, 1-cyanoethyl-2-phenylimidazole,1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, guanamine, acetoguanamine,benzoguanamine, amine, dicyandiamide, benzyldimethyl amine,4-(dimethylamino)-N,N-dimethylbenzyl amine, 4-methoxy-N,N-dimethylbenzylamine, 4-methyl-N,N-dimethylbenzyl amine, melamine, phenolic resin,phenol novolak resin, and cresol novolak resin.

In one embodiment, the conductive polymer is inherently or naturallyconductive. In one embodiment, the conductive polymer is selected from agroup consisting of polyaniline, polypyrrole, and polythiophene,polyphenylenevinylene, polydialkylfluorene, polyaniline derivatives,polypyrrole derivatives, polythiophene, derivatives, and a nanocompositepolymer. The conductive material can also be Iodine (AsF5),polyacetylene, or poly sulfur nitride with dopant.

In one embodiment, the lithographic reactive component is a monomer, adimer, or a short chain oligomer having ethylenic unsaturation. Thelithographic reactive component may be selected from a group consistingof styrene maleic anhydride copolymers, and similar anhydride-containingcopolymers, wherein each of the styrene maleic anhydride copolymer, andthe similar anhydride-containing copolymers is partially esterified withhydroxy-functional (meth)acrylic esters. In one embodiment, thehydroxy-functional (meth)acrylic esters is selected from a groupconsisting of hydroxyethyl acrylate, acrylic acid, methacrylic acid,maleic acid, fumaric acid, and citraconic acid functional monomers.

In one embodiment, the photo-active material is selected from a groupconsisting of 9-phenylacridine, n-phenyl glycine, aromatic ketones,N,N′-tetraethyl-4,4′-diaminobenzophenone, and4-methoxy-4′-dimethylaminobenzophenone. The aromatic ketones can bebenzophenone, N,N′-tetramethyl-4, or 4′-diaminobenzophenone.

A surfactant may also be included in the additives. In one embodiment,the additives are selected from a group consisting of a color former, asurfactant, a catalyst, a filler, a plasticizer, and a metal powder. Theadditives can be component that will enhance the conductivity of thepolymer. Materials that can be used as additives also include aconductive agents, metals, metal powders, and nanosize metal powders.The conductive materials can be copper, gold, titanium, chromium,aluminum, iron, nickel, cobalt, zinc, copper zinc, nickel-iron,cobalt-iron, silver, Graphite, or carbon black powder, etc.

A solvent is included in the mixture that makes the conductivelithographic polymer. The solvent can be selected from various types ofsuitable organic solvents including a hydrocarbon solvent or an alcohol.The organic solvent can also be selected from a group consisting ofketone, methyl ethyl ketone, cyclohexanone, aromatic hydrocarbon,toluene, xylene, tetramethyl benzene, glycol ether, diethylene glycolmonoethyl ether, dipropylene glycol diethyl ether, ester, ethyl acetate,butyl acetate, butyl cellosolve acetate, carbitol acetate, aliphatichydrocarbon, octane, decane, petroleum solvent, petroleum ether,petroleum naphtha, and solvent naphtha.

The conductive photolithographic polymer has a conductivity comparableto that of a conductive metal such as copper, iron, nickel, cobalt,zinc, copper zinc, nickel-iron, or cobalt-iron. The conductivity of theconductive photolithographic polymer can be brought up the conductivityof these conductive metals by varying the concentration of the additivesor the metal powder. In one embodiment, the conductivity of theconductive photolithographic polymer ranges from about 1×10⁻¹⁰ to about1×10⁶ Siemens per centimeter. Generally, copper has a conductivity levelof about 1×10⁶ Siemens per centimeter and a semiconductor material has aconductivity level of about 1×10⁸ Siemens per centimeter to about 1×10²Siemens per centimeter.

Films, patterns, or lines formed using the conductive lithographicpolymer can be achieved using lithographic techniques currently used indevice fabrication. Standard lithographic printing technology can beused to fabricate films, lines, or patterns of the conductivelithographic polymer on various substrates. After the fabrication, thesefilms, lines, or patterns of the conductive lithographic polymer mayform conductive features or metalization for various semiconductor orelectronic devices. The conductive lithographic polymer can be formed ona substrate from an ink, a solution, or a dry film with a deposition,printing, or lamination process. The conductive lithographic polymer canbe used in the fabrication of an electronic device, a micro-electronicdevice, a microprocessor, a chipset, an electrical controller, a printedcircuit board, an electrical appliance, an optical coupler, anoptoelectronic component, a display component, a liquid crystal display,or a flat panel display, etc., which may all use the conductivelithographic polymer in their circuitry.

In one embodiment, an electronic device such as a printed circuit boardis formed using a conductive lithographic polymer such as thosepreviously described. It is to be noted that the exemplary mixtures ofthe conductive lithographic polymer previously mentioned are not theonly components that can be used for the conductive lithographic polymerused in making the electronic device. The fabrication of an electronicdevice that may benefit from the conductive photolithographic polymerwill be described with reference to FIGS. 2A-2D.

First, an insulating layer 250 having an opening 240 as a via or athrough hole is formed on each of both (top and bottom) surfaces of acore substrate 200 (FIG. 2A). The substrate 200 can be any desiredsubstrate such as an organic material, ceramic, glass, or semiconductormaterial such as silicon, silicon containing material, silicon oninsulation material, silicon germanium material. The substrate 200 mayinclude microelectronic structures such as transistors or integratedcircuits (not shown) formed thereon or therein.

The substrate 200 also includes conductive features 202. The conductivefeatures 202 can be formed on the top surface, side surfaces, and bottomsurface of the substrate 200. The conductive features 202 can be aconductive contact or contacts or metalization layers for the devices(not shown) that have been formed in the substrate 200 such as atransistor or an integrated circuit using methods known in the art. Theconductive contacts can be made of copper, titanium, aluminum, chromium,or other suitable conductive material.

The insulating layer 250 is a conventional dielectric or insulatingmaterial typically used in semiconductor devices. The insulating layer250 is formed on the substrate 200 using conventional methods as is knowin the art. Vias or through holes 240 are created into the insulatinglayer 250 so that electrical contacts can be established to theconductive features 202. The insulating layer 250 can be formed on bothtop and bottom surfaces of the substrate 200 depending on applicationsand devices.

Next, a conductive photolithographic film 230 is formed on a surface ofthe insulating layer 250 (FIG. 2A). In one embodiment, the conductivephotolithographic film 230 is formed on both top and bottom surfaces ofthe insulating layer 250. In one embodiment, the conductivephotolithographic film 230 is formed from an ink solution where theconductive photolithographic material is printed or laid down on thesurface of the insulating layer 250. The printed conductivephotolithographic material is then allowed to dry or cure to form theconductive photolithographic film 230. Alternatively, the conductivephotolithographic film 230 is formed by laminating a dry film down ontothe surface of the insulating layer 250. Pressure and temperature may beapplied to cause the conductive photolithographic film 230 to flow intothe vias or through holes 240 to contact the conductive features 202.

Next, the conductive photolithographic film 230 is masked (FIG. 2B witha mask 241) according to a desired circuit pattern for the film 230using methods known in the art similar to masking a photoresist film.The conductive photolithographic film 230 is then exposed to light 245,for instance, at about 50-150 mJ/cm² as typically done in exposing aphotoresist film. Then, the light exposed conductive photolithographicfilm 230 is developed to create the desired pattern of conductivephotolithographic film. The unmasked portion of the conductivephotolithographic film 230 is removed upon the development of the film230 leaving the masked portion of the conductive photolithographic film232 as shown in FIG. 2C. The developing solution can be a conventionaldeveloping solution used to develop a photoresist film as is known inthe art, e.g., a 0.7-1.0% solution of sodium.

The conductive photolithographic film 232 may have a thickness similarto that of a typical electroless plating film used in conventionalprocess for forming conductor paths as previously described. In oneembodiment, the conductive photolithographic film 232 has a thicknessbetween about 0.5 μm to about 10 μm.

The traces of the conductive photolithographic film 232 is also designedor configured such that all traces are connected to external poles (notshown) for electrolytic copper plating. The connecting traces are lateron etched away after the electrolytic copper plating.

Next, an electrolytic plating film 234 is formed on the conductivephotolithographic film 232 (FIG. 2D) using techniques known in the art.For example, the electrolytic plating film 234 can be formed by dippingthe substrate 200 into an electrolytic plating liquid and flowing anelectric current through the conductive photolithographic film 232. Theelectrolytic plating film 234 will be formed on the conductivephotolithographic film 232. The electrolytic plating film 234 may have athickness of about 5-30 μm. The electrolytic plating film 234 istypically an electrolytic plating copper film. In one embodiment, asolution comprising sulfuric acid of about 180 g/L and copper sulfate ofabout 80 g/L is used for the electrolytic plating process to form theelectrolytic plating film 234. Together, the electrolytic plating film234 and the conductive photolithographic film 232 form conductivepatterns or circuit patterns 236 of the semiconductor device. In theembodiments where the conductive photolithographic film 232 is formed onthe top and bottom surfaces of the substrate 200, the electrolyticplating film 234 may also be formed on both top and bottoms surfaces ofthe substrate 200 as shown in FIG. 2D. After the electrolytic plating,the traces connected to external poles used for the electrolytic platingare etched away using a conventional method.

The process illustrated FIGS. 2A-2D can be repeated as many times asnecessary for forming additional layers of conducting patterns for amultilayer semiconductor devices. For instance, another insulation layer247 can be formed on top of the substrate 200 and over the conductivepatterns 236 as shown in FIG. 2E. Vias/holes 249 are created through theinsulation layer to allow for connection to the conductive patterns 236or other conductive features on the substrate 200. Then, the processdescribed for forming the conductive photolithographic film and theelectrolytic film previously described can be likewise repeated tocreate another desired circuit pattern.

In one embodiment, the conductive features 202 shown above can also bemade from a conductive lithographic polymer. In the present embodiment,a conductive lithographic polymer such as those previously described (inthe form of an ink or a dry film) is formed, deposited, or laminated onthe substrate 200 to form a conductive lithographic polymer film. Theconductive lithographic polymer film is then masked, exposed, anddeveloped similar to previously described to form a desired circuitpattern for the conductive features 202. After the conductivelithographic polymer film is patterned, the conductive elements 202 areformed on the substrate 250. In the embodiment where the conductivelithographic polymer is laid down as a film, pressure and temperaturemay be applied to cause the conductive lithographic polymer film to flowinto crevices, openings, trenches, or vias (not shown) on the substrate200.

In the embodiments above, the conductive lithographic polymer is used toreplace the electroless copper process and the photoresist process asused in the conventional method to form conductive patterns. In someother embodiments, a conductive lithographic polymer is used to replacethe electroless copper plating, the photoresist, as well as theelectrolytic copper plating as used in conventional methods of formingconducting patterns. FIGS. 3A-3C illustrate such embodiments. In theseembodiments, a conductive lithographic polymer film is first formed on asurface of a substrate. The conductive lithographic polymer film is thenmasked, exposed, and developed to form a conducting pattern. Theconductive lithographic polymer film is formed sufficiently thick andwith sufficient conductivity so that the electrolytic plating is notnecessary.

In FIG. 3A, an insulating layer 350 having an opening 340 as a via or athrough hole is formed on a surface (as shown herein, each of the topand bottom surfaces) of a core substrate 300. The substrate 300 can beany desired substrate such as an organic material, ceramic, glass, orsemiconductor material such as silicon, silicon containing material,silicon on insulation material, silicon germanium material. Thesubstrate 300 may include microelectronic structures such as transistorsor integrated circuits (not shown) formed thereon or therein. Thesubstrate 300 also includes conductive features 302. The conductivefeatures 302 can be formed on the top surface, side surfaces, and bottomsurface of the substrate 300. The conductive features 302 can be aconductive contact or contacts or metalization layers for the devices(not shown) that have been formed in the substrate 300 such as atransistor or an integrated circuit using methods known in the art. Theconductive contacts can be made of copper, titanium, aluminum, chromium,or other suitable conductive material.

Next, a conductive photolithographic film 330 is formed on a surface ofthe insulating layer 350. In one embodiment, the conductivephotolithographic film 330 is formed on both top and bottom surfaces ofthe insulating layer 350. In one embodiment, the conductivephotolithographic film 330 is formed from an ink solution where theconductive photolithographic material is printed or laid down on thesurface of the insulating layer 350. The printed conductivephotolithographic material is then allowed to dry or cure to form theconductive photolithographic film 330. Alternatively, the conductivephotolithographic film 330 is formed by laminating a dry film down ontothe surface of the insulating layer 350. Pressure and temperature may beapplied to cause the conductive photolithographic film 330 to flow intothe vias or through holes 340 to contact the conductive features 302.The conductive photolithographic material may fill into the openings,vias, trenches, or crevices after being formed on the insulating layeras shown in FIGS. 3A-3C.

Next, the conductive photolithographic film 330 is masked (FIG. 3B) witha mask 362 according to a desired circuit pattern for the film 330 usingmethods known in the art similar to masking a photoresist film. Theconductive photolithographic film 330 is then exposed to light 360, forinstance, at about 50-150 mJ/cm² as typically done in exposing aphotoresist film. Then, the light exposed conductive photolithographicfilm 330 is developed to create the desired pattern of conductivephotolithographic film. The unmasked portion of the conductivephotolithographic film 330 is removed upon the development of the film330 leaving the masked portion of the conductive photolithographic film332 as shown in FIG. 3C. The developing solution can be a conventionaldeveloping solution used to develop a photoresist film as is known inthe art, e.g., a 0.7-1.0% solution of sodium.

The conductive photolithographic film 332 may have a thickness similarto that of a typical electroless plating film plus a typicalelectroplating film used in conventional processes for forming conductorpath as previously described. In one embodiment, the conductivephotolithographic film 332 has a thickness between about 10 μm to about100 μm.

The process illustrated in 232 FIGS. 3A-3C can be repeated as many timesas necessary for forming additional layers of conducting patterns for amultilayer semiconductor devices. For instance, as shown in FIG. 3D,another insulation layer 347 can be formed on top of the substrate 300and over the conductive patterns 332. Vias/holes 349 are created throughthe insulation layer 347 to allow for connection to the conductivepatterns 332 or other conductive features on the substrate 300. Then,the process described for forming the conductive photolithographic filmcan be likewise repeated to create another desired circuit pattern.

In one embodiment, the conductive features 302 show above are made froma conductive lithographic polymer. In the present embodiment, aconductive lithographic polymer such as those previously described (inthe form of an ink or a dry film) is formed, deposited, or laminated onthe substrate 300 to form a conductive lithographic polymer film. Theconductive lithographic polymer film is then masked, exposed, anddeveloped similar to previously described to form a desired circuitpattern for the conductive features 302. After the conductivelithographic polymer film is patterned, the conductive elements 302 areformed on the substrate 300. In the embodiment where the conductivelithographic polymer is laid down as a film, pressure and temperaturemay be applied to cause the conductive lithographic polymer film to flowinto crevices, openings, trenches, or vias (not shown) on the substrate300.

Embodiments of the present invention may be used to reduce the longprocess throughput time for semiconductor device fabrication caused byelectroless and electrolytic processes. Additionally, the embodimentsmay allow for reducing of materials used in fabrication intermediatesteps (e.g., photoresist material and electroless plating materials)typically used for coating and etching processes.

While the invention has been described in terms of several embodiments,those of ordinary skill in the art will recognize that the invention isnot limited to the embodiments described. The method and apparatus ofthe invention, but can be practiced with modification and alterationwithin the spirit and scope of the appended claims. The description isthus to be regarded as illustrative instead of limiting.

Having disclosed exemplary embodiments, modifications and variations maybe made to the disclosed embodiments while remaining within the spiritand scope of the invention as defined by the appended claims.

1. An electronic device comprising: a substrate; a dielectric layer overthe substrate; a patterned conductive photolithographic film over thedielectric layer, the patterned conductive photolithographic film havinga portion that has been removed, wherein the patterned conductivephotolithographic film is patterned by development, and wherein thepatterned conductive photolithographic film has a characteristic that itis not removed during the development, and wherein the patternedconductive photolithographic film comprises a reaction product of anepoxy acrylate; and a metal film plated on the patterned conductivephotolithographic film.
 2. An electronic device comprising: a substrate;a dielectric layer over the substrate; a patterned conductivephotolithographic film over the dielectric layer, the patternedconductive photolithographic film having a portion that has beenremoved, wherein the patterned conductive photolithographic filmcomprises a photo-active material, and wherein the photo-active materialcomprises at least one of 9-phenylacridine, n-phenyl glycine, aromaticketones, N,N′-tetraethyl-4,4′-diaminobenzophenone, and4-methoxy-4′-dimethylaminobenzophenone; and a metal film plated on thepatterned conductive photolithographic film.